Fixed: Unable to select option in combobox in IE and Chrome
    
    There's probably a bug regarding z-index stacking in Chrome and IE. It appears when combobox is used in dialog. Combobox's select area had z-index=1010. When first jquery dialogs is open it has z-index=1000. Further dialogs have higher z-index. When dialog's z-index exceeds 1010 option in select control can't be selected. IMO it is a browser bug because select control lies in dialog content's stacking context so it should be functional even with z-index=1.
    
    This patch raises select area's z-index to 9000000 which should prevent the issue for some time. Also it make's combobox's z-index configurable so we can solve combobox stacking (ie in service-add dialog).
    
    Second part of:
    https://fedorahosted.org/freeipa/ticket/2834